Ancient China was a place小题1: _______ states were often 小题2: ______ war with each other. But it was also a time 小题3:_______ there were many great philosophers. Confucius (55I BC --- 479BC ) is the philosopher小题4: ________ influence has been the greatest. He stressed the importance of kindness, duty and order in society. Chinese society was influenced by these ideas for more than 2000 years. Mencius was a thinker whose teachings were very similar to 小题5: ________ of Confucius.

What will the city of the future look 小题6: _______ ? No one knows小题7: ______ sure, and making predictions is a risky business. But one thing is certain ----- they are going to get bigger 小题8: _______ they get smaller. In the future, care for the environment will become very important 小题9:______ earth’s natural resources give out. We will use lots of recycled materials, such as plastic, aluminium, steel, glass, wood and paper, and we will waste fewer natural resources. We will also have to rely more 小题10:________ alternative energy, such as solar and wind power.

在科技小组活动中亮亮同学受图1所示电子秤的启发，自行设计了一个电子秤，其原理如图2所示，他试图用电压表（图中暂没画出）的示数来反应物体质量的大小．设电源的电压为恒定U，定值电阻的阻值为R₀，滑动变阻器的总电阻为为R，总长度为L，滑动触头固定在安放托盘的轻质弹簧上，并能随轻质弹簧一起自由滑动，已知对托盘每施加1N的压力时，弹簧的长度就会缩短a．当托盘中不放物体时，滑动触头指在最上端，此时电表的示数为零；当在托盘中放一物体时，滑动触头随弹簧向下移动到某一位置，于是电压表就指示出相应的示数．

（1）若在托盘上放一质量为m的物体，则滑动触头向下移动多大的距离？

（2）请在原理图的适当位置接上符合要求的电压表；

（3）求出电压表的示数U_表与待测物体质量m之间的关系式（用已知量的符号表示）．